This invention relates to locks which have settable elements like disks, levers, or other forms of "tumblers" that can be set by a key.
Nearly all locks can be described, in a general sense, in the following way. They consist of an external memory which can be a key or a card or simply the intelligence of the operator. The lock is provided with an internal memory which can be set into coincidence with the external memory. There must be a provision by which the two memories can be made to interact. This can either be a slot in the lock through which a key can enter, or a slot for a card, or a dial or knobs to be operated manually by the user. In some recent technology, this interaction can even be a device that reads the fingerprint, the size of the user's hand, or any other arrangement of sensors that can connect the outside world to the inside memory of the lock.
The lock has a fourth major device that can detect the coincidence between the outside and inside memories. If the coincidence is correct, this fourth element permits the lock to open. This may be an electronic device that provides the proper signal, and it may be a mechanical component that permits a cylinder lock to turn, or a mechanical device that permits a bolt to be withdrawn.
It is obvious that locks can be defeated in one of two principal ways. The first is by brute force; that is, the lock can be broken, cut out, drilled, or otherwise damaged and neutralized. Some such techniques can be quite subtle in that a small hole can be drilled through which the internal mechanism can be examined and manipulated.
The second method for defeating a lock, and the problem addressed in this invention, is the general means called "picking" or surreptitious entry. In this approach, the lock is not damaged in any way, but by use of proper instruments coupled with skill of the operator, the internal mechanism can be manipulated and the lock opened.
In order to defeat this type of surreptitious entry, a great many expedients have been invented. Torque sensing devices, complicated keys, complicated tumblers and disks, time delay mechanisms, and a great many other techniques have been designed and produced. I myself have three patents on such expedients. They are U.S. Pat. Nos. 3,172,283; 4,111,019; and 4,485,648.
U.S. Pat. Nos. 2,528,964; 1,702,430 and 180,255 appear to be related to my subject invention. They discuss the principal idea of blocking the key slot before the lock can be opened. They do not, however, close the key slot completely or isolate the key from the tumblers. In one case, the key is made to have a wide flange and a rather narrow neck so that most of the key slot can be closed, but the passage to the tumblers from the outside world remains open although, as the patent clearly states, the passage is somewhat tortuous. In the others, the key slot is only partially closed.
U.S. Pat. No. 2,179,947 to S. Miller is much closer to the subject of my invention. Here a small key is inserted into the lock and is completely "swallowed" before it can be opened. The key slot is closed and the lock is turned by a handle. When the action of the lock is finished, the key is ejected from the lock. The disadvantages of having to use a key that cannot be conveniently carried as a ring or in a key case, that has a very small head, and that can get stuck in the lock because of dirt, congealed oil or a slight bend in the key, are too obvious to need further discussion.